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Adrian Wilson

Editor's Viewpoint

31st October 2017, Munich

Next step in recycling carbon thermosets

Composite waste for recycling at ELG in the UK. © ELG Carbon FibreIn a first for the industry, a semi-commercial pilot plant is currently being constructed in Germany for recycling thermoset carbon composites via solvolysis with supercritical water.

The process is unique in allowing both the fibres and the matrix of these valuable materials to be recovered to a large extent, but has so far only been trialled on a laboratory level at institutes such as the University of Augsburg in Germany.

Speaking at the recent Smithers Rapra Go Carbon Fibre conference in Munich, Professor Volker Warzelhan, chairman of the west regional department of German industry organisation Carbon Composites, said that by 2020, there would be 20,000 tons of valuable carbon fibre waste in Europe and only a third will be scrap that can be re-used.

“Pyrolysis is the only way of dealing with this waste at the moment, but downcycling is not the path we want to go down in the long term, so we have to try and find a solution,” he said.

Solvolysis with supercritical water, he explained, involves a homogenous medium with a high diffusion coefficient and fast kinetics, making possible the hydrolysis of organic molecules for recovering epoxy resins. In comparison to the classical solvolysis process, it can have shorter reaction times of around 30 minutes and is based on just water, as the environmentally friendly solvent. It does, however, require a higher energy input in terms of both pressure and temperature.

Lab scale tests at the University of Augsburg have achieved recycled carbon fibre with mechanical properties close to that of virgin fibre, in addition to high potential for the material recovery of the matrix components.

The new plant under construction has been designed by plant engineering firm Environmental Technologies Exchange (ENTEX) of Schwäbisch Gmünd near Stuttgart, and GESA Engineering und Apparatesysteme of Chemnitz.

The intention at the plant is to manage the high pressure requirement by just heating up the water and to recycle more than 50% of the energy required batch to batch. Sampling at 190ºC and 20 bar will initially be carried out, with the aim of achieving a high throughput for processing 130kg batches. The intended end products are carbon fibre patches, as well as the matrix components.

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